Cenozoic landscape evolution of an East Antarctic oasis (Radok Lake area, northern Prince Charles Mountains), and its implications for the glacial and climatic history of Antarctica

Abstract:

Ice-free areas Antarctica reveal a multi-million year history of landscape evolution, but most attention up to now has focused on the Transantarctic Mountains. The Amery Oasis in the northern Prince Charles Mountains borders the Lambert Glacier—Amery Ice Shelf System that drains 1 million km2 of the East Antarctic Ice Sheet, and therefore provides a record of fluctuations of both local and regional ice since the ice sheet first formed in early Oligocene time. This glacial record has been deciphered by (i) geomorphological mapping from aerial photographs and on the ground, (ii) documenting the relationship between thick well-dated, uplifted glaciomarine strata and the underlying palaeolandscape, (iii) examining surficial sediment facies, and (iv) surface-exposure dating using 10Be and 26Al. The SE Amery Oasis records at least 10 million years of landscape evolution beginning with a pre-late Miocene phase of glacial erosion, followed by deposition of glaciomarine strata of the Battye Glacier Formation (Pagodroma Group) in late Miocene time. A wet-based ice sheet next expanded over the SE Amery Oasis, following which deposition of the glaciomarine Pliocene Bardin Bluffs Formation (Pagodroma Group) took place. Both formations were uplifted; by at least 500 and 200 m, respectively. Their tops are characterised by geomorphological surfaces upon which intensive periglacial activity took place. Higher-level bedrock areas were subjected to deep weathering and tor-formation. Early Pleistocene time was characterised by expansion of a cold-based ice sheet across the whole area, but it left little more than patches of sandy gravel and erratic blocks. Late Pleistocene expansion of local ice (the Battye Glacier) saw deposition of moraine-mound complexes on low ground around Radok Lake and ice-dammed lake phenomena. Subglacial drainage of the lake escaped to the east exhuming the sediment-filled gorges. Holocene landscape modification has been relatively superficial. Overall, the landscape of the Amery Oasis evolved primarily under the influence of wet-based (probably polythermal) glaciers in Miocene and Pliocene times, whereas the Quaternary Period was characterised mainly by cold-based glaciers that had comparatively little impact on the landscape.